200+ WHP NA build

[johnc]

Call it 70 ft-lb/l, and your 3L should make about 210 ft-lb torque, and 7200 RPM works out to 288 hp (thats at the crank). I don't understand how you got 275 ft-lb at any RPM, but I'd like to learn. What I'm thinking is that a high-overlap cam has a sweet-spot in the RPM range where it combines with the manifold length to give a Veff > 1 and so generates a bump in the torque curve

 

I made it a point to say that my engine was not a production engine. But even for production engines I think your rule of thumb is way low. For my particular racing 3L I had the builder optimize the engine for torque with as broad a torque curve as possible. Lots of head work including welding up and re-contouring the exhaust and intake ports so they all flowed the same. Development work on three different custom cam profiles, individual ignition timing for each cylinder through the Motec EMS, custom intake manifold, custom header, etc. It made 285 to 294 whp (depending on the chassis dyno used) and a consistent 325 horsepower on the engine dyno.

 

There was a lot of tuning of intake runner length a taper, header primary size and collector merge, and a lot EMS programming to get the numbers my engine developed. The engine builder said it would have been a lot easier to build a horsepower engine. All the components were there to run the engine to 8,500 rpm but my imposed torque goal made that unnecessary.

 

You should also search for a couple of Tony's posts regarding the L6 harmonics in the 7,000 to 8,000 rpm range. L6 engines are happy below and generally happy above that range. Within that range the harmonics require forged pistons, good rods, and outstanding balancing. For my engine the builder took 15 lbs. out of the crank, 25 lbs. out of the clutch and flywheel, and added a ATI Super Damper.

[Tony D]

"Tony - 205 (crank HP) and 9:1 compression (I'll guess 57 ft-lb/l) works out to 9450 RPM - bet it sounded pretty!"

 

Mustive been slightly higher than 9:1 then... As a world record holder you would think it was a 'race' engine, huh?

[Bob_H]

Not to belabor this, but you took a general statement for a production engine (that is: an engine built by a manufacturer for every day use, with a CR around 9-10:1) and tried to apply it to a what is essentially a racing engine. The rest of my text says CR is the major factor affecting torque/liter. 13.6 should give about 12-15% higher torque/L - and all the little tweaks done to a high-performance engine adds a bit more. Call it 70 ft-lb/l, and your 3L should make about 210 ft-lb torque, and 7200 RPM works out to 288 hp (thats at the crank). I don't understand how you got 275 ft-lb at any RPM, but I'd like to learn. What I'm thinking is that a high-overlap cam has a sweet-spot in the RPM range where it combines with the manifold length to give a Veff > 1 and so generates a bump in the torque curve.

 

.....

 

Finally, if my estimates are low, the worst thing that happens is I build a motor that makes more power than I had hoped for. That ain't so bad...

 

Don

 

 

Don,

We are all trying to help you spend less money than you seem to want to for your desired goal. You can certainly build a 7500 rpm motor - it requires a builder familiar with the L6 and good at what they do. That is a very long crank and as John and Tony in other posts have alluded to - it has some interesting harmonics in the 7-8k range.

 

Forgive me for being blunt - ok, don't forgive me. Your being obtuse and missing the point here. You aren't an engine builder, you haven't built one of these before, and you don't do this for a living. Your an armchair engineer on this issue. You have many of us who HAVE built these motors well in excess of your modeling. Many of us are engineers as well - some for their full time job. Many of us can also tune the EFI motors. We aren't speaking out of theory and conjecture - but actual experience.

 

If you are hard on up 7500 rpm because your calculations say for 200 hp you need that for a 2.8L motor - by all means spend your hard earned money. Bottom line - you don't need to spend that kind of cash to achieve those goals. Your model is not accurate - and we could spend plenty of time showing you example after example that don't follow it to every one you find that does. The current crop of LS motors are a prime example. STOCK LS3 from a corvette - 6.2L motor, 424 lb-ft of torque per the factory rating. VERY easy to increase that by a significant margin - but the STOCK setup means your model predicts 372 lb-ft vice the actual 424.

Its a factory motor with 68+ lb-ft per liter, or 13% over your theory. There are many daily driver LS motors that are pushing near 600 lb-ft of torque at the motor - or nearly 100lb-ft/l and 60% more than your model. Bottom line, those may be current technology motors, but they don't anywhere near comply with your model.

 

By that same token - your using data from builds that you don't know the extent of the prep, knowledge level of the builder on the L6 motor and heads/etc.. Its a crap shot. A competent builder of L6 motors,(Rebello, Sunbelt when they were doing it, and a few others I know), with good money spent on a head - yield results well exceeding your model. See the trend and why we are giving you such a hard time? I can take a great $$$$$ head and put it on a shortblock that was not well prep'd,(unbalanced/etc..), and the output will go down a significant amount. I can have timing off by a little bit and the entire power curve is skewed and lower. I can have the fueling completely off and it will be a piece of crap.

There are so many variables in output its impressive. "Streetable" or 11:1 CR and lower plus driveable,(not 1200+ rpm idle) as you define it means your approximation doesn't work for many motors, not just a few examples. All my NA cars - my LS motored RX-7, My 240Z, and several others I've owned and built all exceed 60 lb-ft of torque per liter by more than a few % - usually by nearly 40-60%.

You want a fun to drive car, 200+ rwhp, and near torque out of a 2.8L - you flat out don't need 7500 rpm unless you feel a desire to spend more money. You don't need big money - its fairly easy to do. I guess you've already figured out in your mind that its harder to do, or want to justify why you need to spend more than you actually do - we are spinning our wheels here so please admit such and we can move on.

As long as you continue to insist on your model and why you need 7500 rpm, we will continue to show the error of that thinking for your goals.

My suggestion - settle on 7k, find combo's that have worked for 200+ rwhp at that range, and enjoy the heck out of a car that will turn low 13 sec or faster 1/4 mi times, sound incredible and be a blast to drive. SU's or Triples are a cost consideration. I personally like the FI SU throttle body option. Tuning FI is intimidating at first, but with some good solid classes like Greg Banish's engine tuning class - things don't seem so bad. 170 rwhp will yield high 13's for a poor driver in a 240z - faster if your good. 200 or more rwhp is even more fun in a 2500lb car. There aren't many cars that can keep up with a low 13 second or faster car. They are out there esp. the newer cars - but that's pretty good company for a 30+ year old car and 40+ year old motor design technology.

This is a one circle discussion - both going in the same direction with different objectives. One defensive - one offensive. We are on your team and trying to save you money, time and frustration that most of us have gone through at one time,(or multiple times), ourselves. There is some tremendous experience and voices speaking in this thread - might be worth considering why you have some very experienced posters saying your assumptions might not be accurate or correct.

Have you driven a triple carb 2.8L that was tuned well - i.e. 180 or more rwhp? Might change your mind on what you HAVE to build as far as RWHP.

-Bob

[Tony D]

"Forgive me for being blunt - ok, don't forgive me. Your being obtuse and missing the point here. You aren't an engine builder, you haven't built one of these before, and you don't do this for a living. Your an armchair engineer on this issue. You have many of us who HAVE built these motors well in excess of your modeling. Many of us are engineers as well - some for their full time job. Many of us can also tune the EFI motors. We aren't speaking out of theory and conjecture - but actual experience."

 

Usually I'm the guy that reaches this point first...

 

[Gollum]

2011 Ford Mustang GT - 78lbs of torque per liter. 11:1 compression, 4 valve DOHC

 

2000 Honda S2000 - 76.5 lbs per liter. 11:1, 4 valve DOHC

 

1993 300ZX Non-Turbo - 66lbs per liter. 10.5 4 valve DOHC

 

1998 Corvette - 61lbs per liter. 10.5 2 valve OHV

 

 

I just thought that might be an interesting comparison to lay out there for people. It's amazing to me that one might only expect a PRODUCTION range of torque when building a motor for a hot street setup. All those motors can make MORE torque if desired.

 

Torque is directly tied to two main factors. There's cylinder filling, aka volumetric efficiency, then there's combustion efficiency (how much power is being made for a given CFM flow). Almost any motor can reach 100% VE with the right intake, exhaust and cam. It's hitting it for a broad range or high in RPM that's usually quite difficult. Getting a big block isn't actually all that difficult to reach 100% VE in when your target range is 2,000rpm. Then you can combustion efficiency which is highly affected by compression as well as timing, and how much timing an engine needs/likes. While lowering compression might mean less power, you can also run more timing. And while more compression might make LESS power in some cases due to the timing needing to be pulled from a ping happy setup, extra cam can prevent low rpm ping and push the powerband up, giving more overall power and making a compression ratio work.

 

There's even a lot more to it than that which I haven't touched on. But my point is just to draw out again, that it's all about a SYSTEM that creates a setup. Not a parts list. With the right SYSTEM 80lbs of torque per liter isn't impossible, and you can even leave a stock longblock unmodified and even leave it in your engine bay while you do what's needed to make well over 200hp.

[Tony D]

" and you can even leave a stock longblock unmodified and even leave it in your engine bay while you do what's needed to make well over 200hp. "

 

I think someone else said that already...several times.

 

The trees are in the way...

[DeLorean]

Sorry, I bring no form of technical knowledge to this thread so I promise to keep it short. This thread has helped changed my mindset in regards to modding my Z's engine. I originally was going to go RB25, had 90% of the parts but bailed on the project. The more I read these pages the more I realize how much of an idiot I am.

 

I would personally be thrilled with 180-200 at the wheels, and it seems to me that with an L28, SUs and some tuning I could be in that neighborhood. Sure I'd like triples, sure I'd like to go turbo, but money and time aren't on my side. Neither is experience haha.

 

You guys blow me away with your knowledge, I don't want to thread jack anymore than I already have, so I am off to do some more reading and searching.

 

Thanks for the great info posted here, this info is probably stickied throughout HybridZ, but at the very least I'm bookmarking this one.

[Gollum]

The trees are in the way...

 

I thought I was a tree killer? My bad...

[zredbaron]

Don,

 

Save your money and listen to the passel of world-class experts here on HybridZ. Many of the members replying to your thread are among the most experienced and educated minds out there in the L6 motor niche.

 

I used to think I was smart enough to figure it out on my own, but four engine *RE*builds later, I now know that I was given the answer all along, I just didn't like the answer. (Not a good reason!) It wasn't that I didn't believe them, it was that I thought my solutions would also work. I may very well *be* smart enough, but intelligence requires experience to be of any value. When was the last time conjecture was worth your hard-earned dollars?

 

In short, even if you had read books or taken classes on a subject... would you tell a lawyer how to present a case, an airline pilot how to get you there, or a surgeon how to repair your body? Then why be any different with engines? The wealth of *experience* on HybridZ is priceless. And it also happens to be free... if we're able to swallow our pride and hear it.

 

Don't be like me and waste years and thousands of dollars to realize such a mistake...

 

,

Mark

 

PS - Great thread, guys.

Edited September 20, 2011 by zredbaron

[Tony D]

"if we're able to swallow our pride and hear it."

 

I've mentioned this to people for quite a while. Usually they think people telling them what they don't want to hear are some sort of arrogant pricks pontificating to hear themselves speak and make themselves feel superior (at least in my case that's what they think...)

 

But really, many people don't have a clue that many of these guys who are talking knew when to shut up, sit down, and LISTEN to fat old white guys tell it the way it is...

 

I can't count the guys who answered my questions in what now would be considered 'abusive' or 'condescending' manners, when in fact this was just the way the guys had it handed to them.

 

You can lead a horse to water, you can't make him drink. The only thing you can hope is once they have gone and sampled all to wells with dead goats in them, they finally are rewarded with the sweet sweet clear cool water of a great engine build and will share with others their pains from along the way.

 

MANY DON'T!

[middleagedcrazy]

2011 Ford Mustang GT - 78lbs of torque per liter. 11:1 compression, 4 valve DOHC

 

2000 Honda S2000 - 76.5 lbs per liter. 11:1, 4 valve DOHC

 

1993 300ZX Non-Turbo - 66lbs per liter. 10.5 4 valve DOHC

 

1998 Corvette - 61lbs per liter. 10.5 2 valve OHV

 

 

I just thought that might be an interesting comparison to lay out there for people. It's amazing to me that one might only expect a PRODUCTION range of torque when building a motor for a hot street setup. All those motors can make MORE torque if desired.

 

Torque is directly tied to two main factors. There's cylinder filling, aka volumetric efficiency, then there's combustion efficiency (how much power is being made for a given CFM flow). Almost any motor can reach 100% VE with the right intake, exhaust and cam. It's hitting it for a broad range or high in RPM that's usually quite difficult. Getting a big block isn't actually all that difficult to reach 100% VE in when your target range is 2,000rpm. Then you can combustion efficiency which is highly affected by compression as well as timing, and how much timing an engine needs/likes. While lowering compression might mean less power, you can also run more timing. And while more compression might make LESS power in some cases due to the timing needing to be pulled from a ping happy setup, extra cam can prevent low rpm ping and push the powerband up, giving more overall power and making a compression ratio work.

 

There's even a lot more to it than that which I haven't touched on. But my point is just to draw out again, that it's all about a SYSTEM that creates a setup. Not a parts list. With the right SYSTEM 80lbs of torque per liter isn't impossible, and you can even leave a stock longblock unmodified and even leave it in your engine bay while you do what's needed to make well over 200hp.

 

Its amazing to me that I seem to be the only person that knows what an "estimate" is. Maybe I should blame the schools or pocket calculators or something. Estimates are approximate answers, and there are always exceptions when something is different than the estimate is based on.

 

Lets look at Gollum's counter examples.

 

The 98 Corvette actually agrees with my rule of thumb (10:1 CR -> 60 ft-lb/L).

 

All the examples that don't agree are 4-valve DOHC motors.

 

The Honda S2000 is interesting because if you look at dyno charts you see a two-step torque curve; its a pretty mild 60 ft-lb/L (or less) up to 5800RPM, where the VTEC shift the cam lobes and - shazam - 75 ft-lb/L. What might that tell us? Maybe that radical cam timing cam make some good numbers at high-RPM, but it really stinks at low-RPMs (otherwise why go to all the complexity of VTEC?) This might be really interesting if I could build a VTEC L6.

 

The new Ford V8 is similarly interesting. It doesn't have a traditional nearly flat torque curve; it starts relatively low (60 ft-lbs/L) at 2000 RPM and climbs steadily to a peak of 78 ft-lbs/L around 4500RPM, and then tapers back into the low 60s by 7000RPM. Turns out the Coyote can independently control the timing of the intake and exhaust cams; cool - you can put an aggressive grind on the cam and then advance/retard them to fine tune the valve timing.

 

 

I couldn't find any dyno charts for a stock 300ZX; my rule of thumb would have been around 62 or 63 ft-lb/L, Gollum says max torque is 66 ft-lb/L. I'll hazard a guess that the torque curve has a bump in the mid-range where the cam/intakes are tuned to make max power. Works fine, but only at that rev-range.

 

LS2 Chevy's are interesting because they are push-rod V8s with no VTEC-like technology and make close to 80 ft-lb/L with an 11:1 CR (thats a crate motor, the ones that Chevy put in Corvettes were only in the 60-70 ft-lb/L range). I don't know how they do it - maybe the engine designer made a deal with the devil or something. I'm guessing an aggressive cam and they cover up the peakiness with EFI and sheer displacement.

 

Bottom line - my "model' isn't perfect, but its not all that far off, and its really pretty good for old-timey 2V fixed-cam-timing engines.

 

Lets take a look the example Tony gave of an L28 with ported heads, low compression, SUs and 182 whp@6500. Lets call that 225 crank-hp, which works out to 182 crank ft-lb and 65 ft-lb/L, admittedly more than I would have guessed.Tony said all this motor would need is triples to hit 200 whp. I agree, but at what RPM? I don't think bigger carbs are going to add torque; they're just going to let this engine rev higher. (200/182) x 6500 = 7150RPM. I still don't see me being too far off about needing 7500RPM to hit the 200 whp mark.

 

As to the SYSTEM jab, I never said that all you needed was displacement and compression. The whole point of coming up with the model was to just find a starting point - an approximate displacement and CR and redline - to help make decisions based on real world experience. If you think trying to use math to understand how an engine works is a bunch of egg-head-theory stuff, its your loss. I'm happy to listen and learn, but if you want me to kiss your ring or something first, then don't bother to share all your valuable knowledge.

 

Don

 

 

 

 

 

 

 

[Bob_H]

I'm going to edit this - I posted this from my iphone and its hard to change things after you posted. I don't believe in hiding what you post by editing - so the removed parts are in quote form at the bottom - the parts I believe don't belong.

 

 

 

How do you explain 255 rwhp at 6500 rpm in my NA L6?

You continue to miss the point- and that simple point is you don't need the rpm you insist you need. Again- it's your money and your the one that can blame your schooling when you insist that your goals,(not ours), can't be made w/o greater than 7000 rpm- also known as the point where your investment goes up a significant amount.

Your model doesn't work for me- as it would limit what I make and claims I just can't make the power I do at the rpm I do.

You have done a fantastic job of staying on the defensive and telling us your estimates don't explain our results.

We tried to share- but our words fall on deaf ears, not our conjecture, but real, tangible results on how you can make your goals.

I'll tell you what- go build what you think needs to be done and come back and show us.

You are going to lengths to stick to your estimates/model.

Here is the real question- Did you post this to learn how it can be done, or did you post this to have us help prove your theory?

Seems to me I can't find anywhere in your posts where you are trying to understand- but rather are clinging to this model you came up with reading magazines, blogs and posts. It's not clear to me.

 

 

Bob

Items that had no place in the above post: So genius- .... I could care less about your model- .....but you refuse to listen to our results.....is where we were wrong.......Your not taking anything anyone has said seriously- but rather ....Did I miss something here? ....What are you really trying to learn here- or what do you hope we learn from you?

Edited September 19, 2011 by Bob_H

[Tony D]

The guy isn't interested in learning, he's here to argue. That is sad. He's taking my words/examples, and putting a spin on them saying nothing of the sort what I said.

 

When I say 182RWHP, lets NOT call it ANYTHING other than 182 RWHP. Unless you stick the engine on an engine dyno with tracebility you DON'T know what the Crank HP is going to be...PERIOD. The problem with ESTIMATES is they can conform to any model you so choose to make your point---whether it's a valid engineering based rational deduction or USWAG. Usually the latter.

 

You don't get it. I'm not wasting my time trying any more. I'd suggest nobody else does either. Do what you want on your car. It's yours.

 

Next time, don't ask for advice if you aren't willing to listen.

 

I would have inflected Bob H's sentence a little differently:

"You have done a fantastic job of staying on the defensive and telling us your ESTIMATES don't explain our RESULTS"

 

The guys that taught me would usually throw a bolt, wrench, or give someone a swift kick in the arse out of the shop at this point.

 

<INTERNET EQUIVALENT>

 

Now, I go back to MY work and cease wasting time on this lost cause. "The Forest can not be seen. All the trees are in the way. I cut them all down and I STILL can't see this Forest, even from the highest stack of cordwood from my clearcutting of these trees. Someone LIED to me! There is no Forest here, I don't think there ever was!"

 

Edited September 19, 2011 by Tony D

[Drax240z]

Keep it civil guys, it's all well and good to disagree... but let's keep it clean. Read the rules if you are confused what that means exactly.

[Gollum]

Lets look at Gollum's counter examples.

 

The 98 Corvette actually agrees with my rule of thumb (10:1 CR -> 60 ft-lb/L).

 

All the examples that don't agree are 4-valve DOHC motors.

 

The Honda S2000 is interesting because if you look at dyno charts you see a two-step torque curve[snipped]

 

The new Ford V8 is similarly interesting. It doesn't have a traditional nearly flat torque curve; it starts relatively low (60 ft-lbs/L) at 2000 RPM and climbs steadily to a peak of 78 ft-lbs/L around 4500RPM, and then tapers back into the low 60s by 7000RPM. [snipped]

 

LS2 Chevy's are interesting because they are push-rod V8s with no VTEC-like technology and make close to 80 ft-lb/L with an 11:1 CR[snipped]

 

Bottom line - my "model' isn't perfect, but its not all that far off, and its really pretty good for old-timey 2V fixed-cam-timing engines.

 

As to the SYSTEM jab, I never said that all you needed was displacement and compression. The whole point of coming up with the model was to just find a starting point - an approximate displacement and CR and redline - to help make decisions based on real world experience. [snipped]

 

The honda motor could make 75lbs much sooner, and the lower cam COULD make 75lbs at that, but Honda usually chooses to go for a semi-economical cam for the bottom end bellow VTEC while the VTEC side has MUCH more duration, plus the extra lift as well.

 

I don't know the exact specs but from what people are saying the Coyote Cam specs are actually fairly mild. The variable timing on the cam should show you though how even a cam can look when it's fairly optimally timed through the RPM range. If it were timed statically to make that 60lbs per liter at 7,000 then it would probably be make MUCH less than 60 lbs at 2,000.

 

The LS2 can make that kind of torque because it's downright the BEST flowing pushrod V8 head that any OEM has ever manufactured. (relative to valve size of course) Combine that with a wonderful chamber that allows a good burn with good quench and you have an engine that can run high CR AND flow like mad. It's why even a LS1 with just a cam doesn't have a hard timing pushing 400+ hp to the wheels with a stock redline, and coincidentally enough, you're looking for 200hp out of nearly exactly half the displacement of a LS1, and you have an extra 800rpm to do it before weird harmonics even come into play.

 

We're all saying the same thing here. Just get the head cleaned up doing some BASIC work to it, run a stock 2.8 bottom end, get a cam that's good for your goals, then match the fuel system to match and you're done.

 

I posted my torque examples to show what PRODUCTION motors are putting out, and those things have ZERO cam lop and pull cleanly through the range. Most of those engines also have restrictive exhausts with catalytic converters which rob power (and torque). They're all examples of starting points, not end goals.

 

A STOCK L28 is pushing a rated 163 lbs stock, equating to 58lbs per liter. That's also at a measly 8.3:1 CR.

 

So if you get a cam that pulls clean torque numbers from 4000-6500 and keeps up to 65lbs per liter to 6800rpm, you've made your goal with just 2.8 liters. To get 65lbs at 6800 I'd expect to be shooting for around 70-73lbs per liter peak at around 5,000.

 

2.8 * 65 = 182 * 6800rpm = 1237600 / 5252 = 235HP * .85 (15% drivetrain loss) = 200HP RWHP

 

Is that mathematical enough? Experience shown in this thread from other members shows that this isn't hard. A datsun L6 with good carb and exhaust breathing has a fiarly flat torque curve. Extra compression and more aggressive cam alone should get you in the ballpark. Personally I'd also have some basic chamber work done anyways, but that's just me. People street drive similar setups all around the world just fine.

 

I think people have a hard time believing it's that easy because they don't believe the L heads actually flow that well, or can flow that well. Looking at port flow data that others have provided (like 1 fast Z) I'd venture to say it's an AMAZING flowing head for what it is. It's not crossflow and wasn't really designed as a "high end" motor from what I can tell. It's not really anything special, but yet with just minor work they can show big gains that get it in the realm of many newer heads, even some DOHC heads at that. It also doesn't help that there's so many that have built motors and made serious design flaw choices in their build and then wonder where the power is. Even as JohnC stated, they had to do running length and taper testing to really fine tune his motor for what he wanted. You have to be willing to change things around and find out what works best for your combo if you want to get the most out.

[zredbaron]

I'll chip in further to offer another perspective and to hear myself talk. Six one-way, half-dozen the other... in the end you get the same result. (In theory, ironically. Too soon? )

 

Personally, I tend to stay away from numerical estimates and was always more interested in the relationships between the parts. I tend to pester the experts asking why this new part or adjustment will or will not bring me closer to my power (and sound, let's be honest) aspirations. (Not all elders appreciate this line of questioning, some see it as challenging their answer, but I digress...)

 

From my technically educated and indirectly experienced (the hard way, as a consumer) perspective, the NA L6 starts to make 'real' power (let's call it the 225-250 whp benchmark) when the parts are all specifically selected to run together. In other words, when the parts are in tune with one another, as opposed to a bunch of haphazard performance add-ons slapped together (stereotypically by buying all the upgrades in the MSA catalog). I know the OP isn't shooting for 225whp, but perhaps another perspective (less numbers, more practicality) may shed some light. The OP has made it clear he values his numbers above all, but there are always silent readers, after all.

 

In my case, I had Sunbelt build the very next head after JohnC paid for all that R&D (still owe you beers for that!). HybridZ is abuzz with "the power is made in the head." I also add that the head alone doesn't produce much power in and of itself; the other parts have to be there, and it has to be tuned. Common sense, perhaps, but still.

 

I then "slapped" a full race-prepped head onto a Nissan Competition (yeah, it's old!) 3.1L bottom end. The cam I selected was NOT the cam that JohnC's R&D had resulted in -- the stroker wasn't compatible with the cam unless the pistons were significantly valve-relieved. The engine breathed through MSA headers and triple DCOEs with 36mm venturis. This resulted in ~200 whp. I also will add that tuning on the dyno, timing only since I didn't bring the jets, produced a 9% increase in hp and a 6% increase in torque. This wasn't even a tune that included A/F adjustment. This is in stark contrast to the OP's claims that tuning accounts for 1-2% of power. Also, peak hp was at about 6300 rpm. This was also a sizeable camshaft jump from about .465" lift with 270 or so duration to .525" lift with 290/274.8 duration.

 

The next upgrade wasn't as big of a jump parts-wise (debatable, the cam is pretty nice). The bottom end was beefed up (forged slugs), but it was the same specs aside from the valve reliefs in the pistons. Unbalanced. The main changes were switching to a Sunbelt cam that the head was built for (not identical to John's, but close), adding about 1.0 to the CR (to a target of 12:1), and going to full race fuel (VP 109) from 100 octane. From what I understand, the cam was responsible for most of the new-found power: 265whp @ 6000 (lower rpm, despite the aggressive increase in duration). My engine is also in contrast from the OP's claims regarding the need for rpm - I experienced a 33% gain in power and a reduction in peak hp rpm, presumably for primarily VE reasons. The cam was still a Sunbelt cam, it had the same lobe separation, etc. Lift went from .525" to .565", and duration went from 290/274.8 to 326/315 duration. This was with the same ignition, same street headers and same carburetors I was using all along. The cam simply realized more flow potential of the street-performance intake/exhaust that the full race head had been patiently waiting for all along. Still is, too.

 

For me, the lightbulb turned on when I had the head off for this year's round of upgrades (undynoed). I had the head flow-tested and was very surprised to learn that my peak flow numbers *exactly* coincided with the lift numbers on my 2nd Sunbelt cam! It was almost as if the cam was profiled for the flow characteristics of Sunbelt's head work, weird! And yes, I realize this is a race head and not what the OP was looking for. Concepts remain.

 

The point of all this, is that from my perspective there wasn't some numerical relationship for me to out-engineer the engineers, but rather good-old-fashioned trial and error (paid for by those before me). If I wanted to sound technical, I would probably say something to the effect that the volumetric efficiency was maximized through careful measurement of flow characteristics and then the cam was profiled to match. You can (and should!) pay for this "VE matching" / "part tuning" to also include the bottom end, intake, and exhaust... "how fast do you want to spend" comes to mind here.

 

Bottom line, for me it's the relationships that matter. Conceptualizing the significance (and assigning proportional value) is worth much more to me in engine-building decision-making than any set of mathematical guidelines. Sure, I recognize that when I consult an engine builder, numbers will ultimately play a part in my engine design. The difference is, I consult the experts for their numbers to meet my conceptual goals, I don't dictate to them what the numbers should be...

 

But hey, that's me. Technique only.

Edited September 20, 2011 by zredbaron

[Bob_H]

That ^^^^^ above is an excellent discussion of what has been bandied about in this thread.

[zredbaron]

Haha, that was the nice way to summarize my / our hot air. I may or may not have had to look up bandied....

 

Edited September 20, 2011 by zredbaron

[johnc]

I had the head flow-tested and was very surprised to learn that my peak flow numbers *exactly* coincided with the lift numbers on my 2nd Sunbelt cam! It was almost as if the cam was profiled for the flow characteristics of Sunbelt's head work,

 

Funny how that works out...

 

Jim Thompson and I talked a long time before we started on my engine build. He wanted to build a cam for the L6 from scratch because, based on his research, all the aftermarket cams he had worked with previously were based on BMW profiles - at least as far as he could determine (at the time he was building the race engines under contract for BMW and Mazda for their World Challenge Touring efforts). A lot of his research effort went into properly modeling the L6 valve train and from that he was able to work with Piper to develop a profile that required less (then OEM) closed spring seat pressure (load) and still be stable to 8,000 rpm. This was after he welded and cut on two different N42 heads and ran them on the flow bench. He actually picked the head that had the lower peak flow numbers but was almost dead on equal for the exhaust ports and dead on equal for the intake ports. This was a two year effort and the engine spent about 20 hours on the engine dyno. from that he made welding and porting templates for the head and had a few cams made. I think all of that is NLA now that Sunbelt is now Kinetic.

[Daemione]

I've enjoyed reading this thread . . . and I honestly believe that all the "conflict" here has a very easy explanation: differences in torque estimates and measurements. I see people quoting manufacturer's engine specs (some of which are known to be generous), others quoting torque on an engine dyno, and others torque @ the wheels using who knows what dyno method. I think the small percentage of difference being fussed about is EASILY explained by the variance in dyno types & methodology.

 

Bottom line, I agree with the OP's usage of a general maximum of torque per liter. For claims of 80+ ft/lbs of torque per liter, I feel it should be pointed out that F1 engines are only slightly more efficient than that.